Radio beacon system



E. LABN EI'AL RADIO BEACON SYSTEM oct, 25, 1949.

Filed March 10, 1945 2 sheets-sheet 1 Nl Umd INVENTORS EM/L E L BIN DONHLD D. 6PM-'6 Oct. 25, 1949.

E. LABIN ET AL.

RADIO BEACON SYSTEM 2 Sheets-Sheet 2 Filed March 10,` 1945 ETH cas e Z)(s//v27rF2 z) IN V EN TORS .eM/1.5 Lne/N DONALD o. GRM-f7 MM, ATTRNEY Patented Oct. 25, 1949 RADIO BEACON SYSTEM Emile Labin, New York, and Donald D. Grieg,

Forest Hills, N. Y., assignors to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application March 10, 1945, Serial No. 581,974

14 Claims.

Thisn invention relates to Vradio beacons and more particularly to radio beacon systems of the oninidirectional type.

Various forms of omnidrectional radio beacons-have been proposed in the past. One such form contemplates the directive transmission of a radio beam rotated about an axis. To the beam are applied modulating signals producing different characteristic signals for the diierent directions of transmission of the beam. This energy is received at one or more receiving points about the beacon. In response to the received characteristic signal energy, the direction of the receiver with respect to the beacon can then be ascertained. If the receiver is mounted on a craft, the craft can then follow a substantially straight line to the beacon by maintaining in the receiver outputthe same characteristic signal.

It isA an object of our invention to provide a radio beacon system in which the beacon signal is characterized by two different signals varying inamplitude relative to one another in accordance with rotation of a beacon beam according to sine and cosine functions respectively.

4It is a further object of our invention to provide a receiver responsive to the transmitted beacon signals for separating the separate sine and cosine signalsv and producing a directional indication in accordance therewith.

It is a further object of our invention to provide a radio beacon system in which the radio beacon transmitter transmits energy producing sine and cosine envelopes at a receiver point and in which a further signal is provided to render these envelopes at the receiver point usable to produce indications in 360 angles.

`It is a still further object of our invention to provide a radio beacon system of the general type outlined above in which the transmitter and receiver apparatus can be converted for operation on signals in the general form of sine and cosine functions.

It is a still further object of our invention to provide a ratiometer transmitter adapter unit for a rotatable radio beacon and/or a receiver indicator supply unit for a radio receiver adapted to cooperate with a known type of radio beacon such as outlined above.

According to a feature of our invention, a ratiometer transmitter adapter unit is provided for modulating the radio frequency energy supplied to a rotatable beam transmitter. This ratiometer adapter unit may comprise three sources of signal energy of different frequencies.

Energy from two of the sources is modulated in sine and cosine envelopes will be transmitted. The third signal supplied is of a constant amplitude and preferably of a value substantially equal to 1/2 the sine and cosine function energy. These three signals are then used to modulate the energy in the radio transmitter, which may take the form of PTM (pulse time modulation), FM (frequency modulation), or AM (amplitude modulation), so that the radiated beam carries along these three modulation functions. The sine and cosine functions are caused to vary in accordance with the rotatable position of the radio frequency beam. As a consequence, the radiation pattern will contain the first and second frequency signals at different ratios for different directions of the transmitting beam.

For cooperation with this beacon is provided a radio receiver unit which will receive and detect the radio frequency beam energy. In the output of the receiver-detector unit, the three lsignals are then separated, for example, by lters tuned to the respective frequencies. These separated signals may then be applied to two combining circuits for subtracting the envelope of the third frequency from the envelopes of the other two. As a result there will be two output energies one proportional to the sine function and the other proportional to the cosine function. These two energies may then be applied to a ratometer to measure the ratio of the energies received producing thereby an indication of direction. Preferably there is provided a means for finding the effective center of the radio beam so that the indicator will show the true ratio between the signal energies at the beam center rather than on the leading or trailing edges of the beam.

A better understanding of our invention and the objects and features thereof may be had from the particular description thereof made with reference to the accompanying drawings, in which:

Fig. 1 is a block circuit diagram of a beacon transmitter and receiver in accordance with our invention; and

Fig. 2 is a set of curves used in explaining the operation of the system in accordance with our invention.

Turning rst to Fig. 1, there is illustrated at I a radio frequency transmitter coupled to a directive antenna 2. Antenna 2 may be of any desired type and preferably produces a unidirectional radio beam. Motor 3 serves through the medium of a shaft 4 to rotate antenna 2 at a predetermined rate thus producing a rotation of the beam. The adapter unit coupled to the transmitter and antenna arrangement for producing signals varying in ratio about the transmitter as the beam is rotated comprises three oscillators 5, 6 and 1 serving to produce different frequencies F I, F2 and F3 preferably within the audio frequency *band-.5. Oscillatorsyf and lIi are coupled to stator coils 8 and 9 of a vario coupler device I0. A rotor II is provided in vario coupler device I cooperating with stator coils 8 and 9.' Rotor I I is driven in synchronism with rotatable e antenna 2 as indicated by the .shaft I2. It Will therefore be seen that the energy, atfrequencyw FI and frequency F2 will vary -in amplitude iin rotor II in accordance with the expression sin @t Where 0 represents the angular speed of rotation of the rotor coil Iland anter1na-2"and:t@repre-v J If these two energies present .inv

Accordingly', at transmitter I the energy from Coil II ",is'appliedover line I3 'and other energy of frequencies FI and F2 is simultaneously applied over 'lines' I t .and lrespectively." The energy supplied in lines I4 'and"'l5"is suchy as to add properly to that 'supplied from coil I I producing envelopes corresponding with those 'shown in Fig. 2,*curve A; at I 1and I'IA respectively, 'the 'oscilla' tion waveform" between the envelopes being omitted"for'purposes of clarity. It'willl be observed that each :of these' curves varies between zero and 'a'fixed k'maximum value. Preferably, oscillators 5 and 6 Vare controlled so that these two :waves are of equal ,amplitudes- The third wave `F3 from oscillator 6 is maintained at a eonstantamplitude E as'shown at ycurve I8 of'Fig. 2 andv is 'applied over aline I9, Fig." 1, to the radio frequency transmitter. Thus inthe transmitted 'radio beam' is provided a complex modulation envelope such'as indicated 'by the double-curves I6,"'I'I and 'I8'of Fig. 2, curve A. Each' of 'th'ese envelopes is of'a different frequency; The 'waveform I6" may'be represented by the expression E(1{sin' 19t) (sin21r'F1t) or the envelope by the expression 'E(1+sin at) curve II' the expression"E(1-I-cos'0t) and 'curve' I8 by thev expression E sin21'rF3t or'the envelope'by E.

Itwill be seen then'thatgin'one rotation of the' beam from antenna" 2, the ratios of energies represented byenvelopesV I6 and 'I 'I will vary continuously.

At a receiver in the eld `ofthe beacon'there` is'provided'an antenna 20a coupledlto a 'receiverdetector unit 20. serves to produce the envelope frequencies as shown at curve A'of Fig. 2; It will be clear, however, that since the entire envelopedoesl not ap'- pear'at any'one point; the receiver vwill intercept only a small angular portiony of the entire sine and cosine wave signals. Ifitis'assumed that the beam is approximately 25 wide then the'portiony of the envelope effective in the output of receiver-detector 20 will be, for example, that portion contained' between lines 2|` and 22 of curve A; Fig. 2. For two'different positions of the receiver'with respectto 'the beacon; other portions contained between ,lines 23j 2,4 'and 25,

26, for example, `will 'be receivedr" The energy in" the output ofLreceiver-'detector `2Ilis separated into its three signal components'F'I, F2 andF3 in" separate filters 21, 28"and 29.' These lters'.

This receiver-detector 'unit 4 ing lters FI, F2 and F3 during the period of receptions may be more clearly seen byireference to'curve'Blof Figf2. In this figure.' taking the component corresponding to the portion between lines 2| and 422, it will be seen that a small poringly, 'the output4 'energy' `from^'fllters Y--21,' 2 8'. andai` 29 Aare combined in combiningvcircuibsl-341011:

produce the envelopeWavesproportional 'toA the pure sine and cosine 'functions as shown infcuxwefr.;

C." These 'combined'i'ener-gies may 'then be apa.

plied lto the 'coils'35rand `3650i *a ratiometerri'l f and will'serve -to move Athe vrotor-"3 8lint'o r'a Vposi-. tion proportional' to-"this received energy;

It is clear that `if'-the envelope'energiesaaree: applied directly'to lthe ratiometer',' the-rotor T38-1e will vary' in positionrover'the width'of-theebeamvqil starting with'the leading "edgeof the-beamfwhen 1.'.- the receiver'rst vbecomes 'sensitive' 7andstopping-t "when ,the'beam passesrthe receiving antennasr Such an indication'then;` instead of 'gi-ving! a Ldii-'ak rect line .to the beacon; indicates y'the edge roffithel? beam'. It'is 'difli'cultfor the pilot or 'operator-atan the receiver to read 'the midpoint offthe pointer swing. It isv 'therefore desirable`1'to'4 provide v'some a means which will'indicate substantiallyfthe-midf position of the beam In'the system as illustrateilgilr this beam; center 'finder' system'comprisesrinte# grating .circuits 39j lIIl'an'd'M' associated-respec-tv tively,.withthe'outputso'lters 21; 28 and 29.

metrical beam` producesreceived energy 'in "'the'f system; the ratio of the'total received energiess is exactly equal to' the ratio of the-"amplitude'ofpf vthe energiesfat 'the mid-portion'cf- 'theeb'eam Thus, 'turning backto Fig. 2," the `areas -underfsegmentsl 3|, 32 and 30" represent `Vthe'integratedd values of 'the 'received' signalsof'frequencies F'I'r F2 and F3'. The energy underfthesefcurvesrepaaA resent then'th'e output'volt'ageof integrators'f39# 4B.and.4l respectively.' The output'"f1"om"'int'e'-I grator` 4 I Vlis 'subtracted''in 'combining Vcircuits T33. an'd"`34"' respectively; from-'the Ioutput energy'of i integrators '39, and 40so that theresultantmure rent 'in' 'coils 35 and' '36"'is proportional' to the ratio" of these integratedf'values 'and' consequentlyf'to" the energy Vat thel` center, of the beam.' It'f'wi-lltherefore be seen vthat with the "transmitter as described above` andA the' particular'receiver'pirw cuit, the position'pfianycraft' with-'respect to;l the beacon mayA readily be'ascertajn'edt While in" the sys-temas 'shown'iwe have'-r indirv cated that the receiver is suchas'to'v respond sharplygproducin'g a'segm'entgZI, 22, `this' action is not necessary to the operation'ofthe system;4 Regardless. of the specific `shapez'or"Width"'of-*the" segment of signals' received, the ratio of the sine' and cosine function 'energies as'receivediwill'prof videl a proper'indication' of :the'centering of'thel beam solong as th'eibuildLup'j-andicuteoi times' of'the receiver' are' substantially symmetrically," related.

Furthermore," while'we'have shown"'the' sigg.; nals as being :distinguished by`` different sub1", frequencies, it"is vclear"that"any oth'er typeof' system for suitably distinguishing the signals may be provided. For example, the signals supplied from the oscillators 5, 6 and 1 may be of pulses of different` widths or may be distinguished by some other characteristic. The essen- -tial feature is that two of these signals vary in accordance with a sine and cosine function so that in the receiver they may be compared for operating the ratiometer. Furthermore, when other types signals are used, selector circuits for separating these signals other than filters as illustrated may likewise be used.

It further should be understood that while we have shown a vario coupler type of arrangement for providing a sine and cosine variation of the transmitted signal, any other type of transmitter system which would provide the desired variation in synchronism With the antenna rotation may be substituted in its stead. Many other variations in the system in accordance with our invention will occur to those skilled in the art. The specific `description of the particular embodiment is given ergy from said beam, means for detecting said received energy, means for separating the three signals in said detected energy, means for subtracting said third signal from the first and second signals, 4and means for comparing the ratios of said subtracted signals to indicate the direction line.

2. A receiver for indicating direction with respect to a received signal in the form of a beam rotatable about a given axis, and having two signals of a given amplitude varying as sine and cosine functions respectively, in accordance with the rotary position of the beam, and a third signal having a value equal to half said given amplitude, comprising means for'receiving energy from said beam, means for detecting said received energy, means for separating the three signals in said detected energy, means for determining the center of said beam, means for subtracting said third signal from the first and second signals to leave pure sine and cosine functions of said signal, and means for comparing theratios of said subtracted signals to indicate the direction line in accordance with the beam center indication.

3. A beacon system for indicating direction of a receiver with respect to a beacon signal, comprising means Afor transmitting energy in the form of a beam rotatable about a given axis, means for modulating the `energy of said beam with two signals varying as sine and cosine functions respectively, in accordance with the rotary position of the beam, and a third signal having a given value, means for receiving energy from said beam, means for detecting said received energy, means for separating the three signals in said detected energy, means for subtracting said third signal from the iirst yand second signals, and means for comparing the ratios of said subtracted signals to indicate the direction line from said receiver to said transmitter.

4. A radio beacon system for indicating the direction line between a receiver and a transmitting beacon comprising a beacon transmitter for transmitting a signal in the form of a beam rotatable about a given axis, means for modulating the energy of said transmitter with two signals of substantially equal amplitudes varying as sine and cosine functions respectively, in accordance with the rotary position of the beam, and a third signal having a value substantially equal to half said equal amplitudes, means for receiving energy from said beam, means for detecting said received energy, means for separating the three signals in said detected energy, means for subtracting said third signal from the first and second signals, and means for comparing theratios of said subtracted signals to indicate the direction line.

5. A radio beacon system for indicating the direction line between a beacon and a receiver, comprising a beacon transmitter for transmitting energy in the form of a substantially symmetrical beam rotatable about a given axis, means for modulating the energy of said transmitter with two signals of substantially equal amplitudes varying as sine and cosine functions respectively, in accordance with the rotary position of the beam, and a third signal having a value substantially equal to half said equal amplitudes, means for receiving energy from said beam, means for detecting said received energy, means for separating the 'three signals in said detected energy, means for determining substantially the center of said received beam, means for subtracting said third signal from the first land second signals, and means `for comparing the ratios of said subtracted signals to indicate the direction line in accordance with the beam center.

6. A radio beacon system comprising first, second and third sources of energy at diicrent given frequencies, said first and second sources producing output energy of the same given amplitude vand said third source producing output energy at a different given amplitude, a rotatable unidirectional antenna system, means for producing sine and cosine function variations respectively, in said rst and second output energies in accordance with the rotatable position 0f said antenna, a radio transmitter, means for modulating lthe energy in said radio transmitter With said varied rst and second signals and with said third signal, and means for radiating said modulated energy from said rotatable antenna.

7. A radio beacon comprising irst, second and third sources of energy at different given frequencies, said first and second sour-ces producing output energy of the same given amplitude |and l,said third source producing output energy at half said given amplitude, a rotatable unidirectional antenna system, Ameans for producing l-l-sin .and l-l-cos variations respectively, in said first and sec-ond output energies in accordance with the rotatable position of said antenna, a radio transmitter, means formcdulating the energy in said radio transmitter with said varied rst and second signals and with said third signal, and means for radiating said modulated energy from said rotatable antenna.

8. A radio beacon receiver f-or receiving energy from a rotatable beam modulated with rst, second and third energies at diiTeren-t given frequencies, said rst and second energies having the same given amplitude and 1+sinand l-l-cos variations respectively, and said third source producing output energy having half said given 'am- 9. A radio beacon system comprising first, second' and third sources of-energy at different giv- Jen'frequenCieS, said first and second'sources Sproducing output energy of given amplitudes and said third source producingoutputrenergy at a different amplitude, means for producing a rotatable unidirectional radiation, meanslfor producing 'sine andcosine function variations respectively, in said first and second Voutput energies' in vaccordance with the rrotatable position "ofi-said unidirectional radiation, a radio ltransmitter, means for modulating -the energy in= saidradio Ytransmittery with said varied rst and second signals and with said third 'si-gnal, means for radiatingsaid modulated energy from lsaid rotatable Aantenna,a radio `receiver for receiving energy from-said transmitter and detecting saidI energy to reproduce energy at said first, second and `thirdsignal frequencies, means for separating said signal frequencies, combining circuits for subtracting energy at said third-signal from the energy of said first and second signals respectively, toproduceV output signal envelopes corresponding to pure sine and cosine functionsfand means `for indicating the ratio ofthe signal output from said combining cir-cuitsy to determine the directive position of said receiver-with respect to said transmitter.

.10. AV radio beacon systemcomprising first, second-and third sourcesfof energy| at different given` frequencies, said first and second sources producing output energy of givenl amplitudes and 4said third source producing outputfenergyMat-a Vdifferent amplitude,means for producing a rotatable unidirectional antenna system,-means for producing sine and cosine Variations respectivey 1y, in said first and second output energies in accordance with the rotatable-position of said antenna, a radio transmitter,means-for modu- 1ating vthe energy in said radio Atransmitter With said varied-first and second signals andwith .said

third signal, means for radiatingsaid modulated energy from said rotatable antenna, Va radio receiver for receiving venergy from said transmitter andidetecting` said energy to reproduce venergy at s'aidrst, second and third signal frequencies,

A'means' for separating said third signal frequencies, integrating means forvintegrating-said first, second andl third separated signals, combining circuits for subtracting energy of said thirdsignal after integration fromthe energyI of said'rst i andi second'signals respectively, to produce output signal envelopes corresponding to pure' sine and cosine functions, and-means forindica'ting the ratio of thev signal output' from said' combining circuits to determine the directiveposition of said receiver with respect to said transrriitter.L

11. A radio beacon system comprising first, `second and third sources of energy `at"'diif -irent given frequencies, said vfirst and second-sources producing output energy of the same given ampli- 'tdeand said third source\fproducing'outputfen-' fergyat half said'"given/amplituddmeans fox-fpmdu'cingrfa-l" rotatable -unidirectional antenna system; rn'eansforprducing l1 and l-l-'cos 'variations respectively;L in said-bflxstwand vsecond output :energies inL accorda-nce 'with the rotatable position of "said antenna, a radiof-transmitter, means for modulatingltheenergy -in` said' radio 'transmitter Withfsaid varied-rstf-i-andasecond signals and lwith said fthird signaL--means for radiating said "modulatedfenexgy: from said rotatable an- -tennagfa radio A1receiver forreceiving energy from said transmitter andLdetecting-s'aid.energy -to reproduce energyfat-said--rst 'fsecond'and third signal 'frequenciesfmeans for separating said signal frequencies, integrating -means for integratingIsaidrstyseeondiand third separated signals, lcombining .circuits Ifor subtracting energy of said thirdfsignalafterintegration i from the energy 4of said lrst andrsecond. signal respective1y,to produce f outputl signalmenvelopes corresponding lto pure I sine'7 andJ -cosi-ne functions, and: means lfor indicating` the` -vratio4 ofwthe signali4 output from said combiningcircuits-r to determine the directiveposition -of said -receivenwith respect to .said transmitters. y

12. A radio beacon comprisingaitransmitter for transmitting a directive radio energy beam, means for rotating said beam, a first means for modulating the energy of `said beamwitha signal varying asa sine function in accordance with the rotary positions of said beam, a second means for modulating 'the-energy With a second signal Varying as a cosine function in accordance-with the rotary 4positions of saidbeam, and a -third signal means for "modulating 'the energy of said beam With athird signal having a substantially constant amplitude.

13.- A radio 'beacon comprising'- a transmitter for transmitting energy in'the form of a rotatable radio beam, a first means "for modulatingthe energy 'of Saidb'ean'rwith a signal of a 'first frequency varying as a sine function in accordance Withfthe rotaryposition of 'said beam, a fsecond mea'nsfor 'modulating the 'energy of said beam with a` si'gnalbf a secondlfrequency"varying Yas a cosine function "in accordance' vvth the rotary positionsof 'said beam', and a 'third' signal means for modulating the' 'ener'gynfsaid beanr withr a signal 'of' av third lfrequencyjhaving a 'substantially constant amplitude equal 'to' half the' swing of saidsinefunction.

vance-With?the rotarypositionsof said: beam, fand a third Asignal'means fori-moduiating theenergy ffof said "beam" Withta Ithird signal 4havingV asubstantial-ly constant-I amplitude equal to halfwsaid given amplitude.

RFERENCES "CITED I The. folio'wirig references: are-nr record in 1th fiiie'liifvethislfpatem: 

